In commercial distillations for the separation of one component or a plurality of components from mixtures containing the same, it is often difficult to achieve the desired degree of purity. A leading example of the difficulty of separating one component from another is the separation of an alcohol from water or from an azeotropic mixture of alcohol and water. Many approaches have been suggested for processing mixtures and azeotrope-containing streams to secure the desired separation of one component of the mixture or azeotrope from another component. In general, these operations have been relatively expensive and, in many instances, not entirely satisfactory.
U.S. Pat. No. 4,906,787 discloses a process for producing diisopropyl ether containing negligible levels of alcohol and water contaminants by first hydrating propylene in the presence of an acidic zeolite. The result of the hydration was an aqueous mixture of ether and alcohol. This aqueous mixture was then passed into a distillation unit operated at conditions effective to provide an azeotropic overhead stream containing mostly ether and only minor amounts of alcohol and water. The azeotropic overhead stream was then passed to an alcohol separation unit of an extraction column which used process feedwater as the extraction medium. Due to the extraction of alcohol from the ether-rich phase, the solubility of water in the ether-rich phase is reduced leading to further loss of water from the ether product. U.S. Pat. No. 4,906,787 also teaches that the alcohol separation unit can be in the form of a decanter with the condensed azeotropic overhead stream separating into an ether enriched upper phase and an aqueous alcohol enriched lower phase.
U.S. Pat. No. 4,345,973 discloses the recovery of ethanol from a fermentation broth by distilling a dilute aqueous alcohol to its azeotrope, distilling the azeotropic mixture using a third component of either an organic solvent or a strong salt solution to break the azeotrope and remove the remaining water, and distilling the resulting mixture to separate water from this third component.
U.S. Pat. No. 3,122,486 discloses a process of using a distillation unit followed by an absorption unit. An alcohol and water mixture was first distilled into a water stream and an alcohol and water distillate stream. The alcohol and water stream was then introduced to an adsorption unit which contained a molecular sieve or ion exchange resin capable of selectively adsorbing water. As the stream containing isopropanol and water moved through the adsorbent, water was adsorbed and removed. A dry alcohol stream was the product removed from the adsorption zone. U.S. Pat. No. 3,122,486 also teaches the use of a swing bed adsorption system that allowed for one bed to continuously remove water from the distillate while the other bed was being desorbed. The water-saturated adsorbent bed was isolated through using a specific valving arrangement in order to provide suction to the bed, thereby removing water vapor from the bed. Once the pressure in the bed undergoing desorption reaches a predetermined low point, a portion of the dry alcohol product from the other adsorption bed that is undergoing adsorption is passed through the bed for backwashing, thereby preparing the bed undergoing desorption to be switched to adsorption.
The two-stage diisopropyl ether (DIPE) production process disclosed in U.S. Pat. No. 5,324,866 teaches that two separation units were required to separate an isopropyl alcohol (IPA) and water mixture, and to separate a DIPE, IPA, and water mixture. The first separation unit was a fractionation unit which separated an IPA and water mixture into a water stream and an IPA stream that also contained some water. The second separation unit was also a fractionation unit and the IPA and water stream from the first separation unit, and an IPA, DIPE and water mixture were separated into a largely DIPE stream and a largely IPA stream.
Applicants are the first to address the need for a process to separate a first component from a second component, e.g., water and an alcohol, by combining the physical separation processes of distillation and adsorption within a single vessel. As discussed above, others have proposed processes which use both a distillation unit and an adsorption unit, or two distillation units. But applicants here have redefined the economics of such two-unit processes since, with applicants' invention, the prior art two-unit systems are no longer necessary, and only one unit is required to carry out the same functions. A significant reduction in capital equipment costs is now possible since, with applicants' invention, one process vessel is eliminated.